The invention relates to close tolerance waveguide assemblies used in antenna arrays and particularly to the configuration of such assemblies along zero electrical current lines in the antenna arrays.
In the construction of antenna array waveguide assemblies, especially those which are used with systems that operate at microwave and millimeter frequencies, it is desirable to form a series of waveguides to achieve precision antenna aperture control. As the operating frequency of a system incorporating the antenna array increases, the tolerance control, or precision, required of the antenna array assembly becomes significantly more difficult to achieve.
Antenna array waveguide assemblies are conventionally constructed by brazing, welding or bonding a series of waveguides into an array assembly. An example of this method of construction is the electronically steered antenna for United States Air Force B-1 aircraft. In general, tolerance accumulation results in poor yield, particularly at microwave and millimeter-wave frequencies. Another method of construction is the machining of plates of metal, stacking these plates to form the array assembly and then brazing, welding or bonding the joints into a finished structural antenna. An example of the use of this technique is the radar antenna used in the TORNADO Euroepan fighter aircraft jointly produced by West Germany, Italy and the United Kingdom. In the use of this construction technique, the separation of the piece parts of the waveguide occurs along regions of high electrical current density, so as to require a continuous weld, braze or conductive bond to provide electrical conductivity. In the process of welding and brazing, significant heating of the hardware to near melting temperatures is involved resulting in physical distortion and poor electrical performance of the antenna array. Conductive bonds are generally structurally inadequate and when combined with structural adhesives the desired array dimensions cannot be achieved without great difficulty, particularly at higher system operating frequencies.
General antenna theory pertaining to the background of the present invention is discussed in Chapter 7 of Microwave Antenna Theory and Design, Massachusetts Institute of Technology Radiation Laboratory Series (Vol. 12), Louis N. Ridenour, Editor-in-Chief, Edited by Samuel Silver, McGraw-Hill Book Company, Inc., 1949 and Chapter 2 of Waveguide Handbook, Massachusetts Institute of Technology Radiation Laboratory Series (Vol. 10), edited by N. Marcuvitz, McGraw-Hill Book Company, Inc., 1951.
The present invention eliminates the need for welding or brazing altogether, so that such problems do not arise. In the present invention, antenna array assemblies, such as rectangular or ridged waveguide configured assemblies, are constructed by combining plates which are formed into a plurality of equal length members (the broadwalls of the resulting waveguide assembly), protruding from and perpendicularly disposed to a structural member (the narrow wall of the resulting waveguide assembly), wherein each such protruding member has two unformed or formed ends. Each such plate, therefore, constitutes a plurality of half-waveguide assemblies. The plates are generally composed of some metal or metal alloy, but could be composed of other materials or combinations of materials, including treated or metallized plastics. The plates are combined by matching each of the ends of the plurality of protruding members of one plate to the corresponding ends of the (equal number of) plurality of protruding members of the other plates. By bringing together the p1ates in this manner, the narrow walls of the waveguide assemblies are formed, so that the half-waveguide openings in each part of the waveguide assembly are aligned with the openings in the matching part of another waveguide assembly to form complete waveguides, which is thus a complete waveguide assembly for use in an antenna array. This alignment occurs at precisely the line where there is zero electrical current in the broadwall of the antenna waveguide assembly so that electrical conductivity is at the juncture of the half-waveguide assemblies not required. The waveguide assemblies must be held together. For example, a small number of metal bolts are used to hold the plates in an assembly with the bolts passing horizontally between waveguide channels. The dividing line of the plates is selected to be the center line of the waveguide channels where no electrical currents exist. Consequently, no welding, brazing or bonding is required. The bolts are used to compress the accurately machined plates into a precision array assembly which is free of distortion and dimensional errors and displays excellent antenna microwave and millimeter-wave frequency performance. The manufacturing yield for the inventive assembly approaches one hundred percent in contrast to the fifty-percent yield when the brazing, welding or bonding process is employed in the construction.